The present invention relates to a color solid state image pickup camera and, more particularly, to a solid state image pickup apparatus capable of correcting the discrepancy of registration, hereinafter termed "registration discrepancy", due to the fixed point discrepancy of a solid state image pickup element of the chromatic aberration of a camera lens. At present, broadcasting stations widely use triple-tube TV cameras. Because of the development of solid state image pickup elements, however, the image pickup tubes are being replaced by multi-disc TV cameras using solid state image pickup elements.
FIG. 7 is a block diagram showing the triple-tube camera as one example of the prior art. An incident ray is separated by a lens 1 and a prism 2 into image signals of primary colors (i.e., red R, green G, and blue B colors), which are individually transformed into electric signals by camera tubes 3. These electric (or image) signals are processed through a video signal processor 4 to generate video signals.
If the centers of the images of the colors separated by the prism of FIG. 7 are not properly aligned with respect to the light receiving faces of the image pickup tubes or if the lens has chromatic aberrations of the like, the positions of the images contained in the video signals are offset. Images which are offset cause individual colors to form a twin image (due to the registration discrepancy), run colors together or decrease the resolution. As a result, quality is deteriorated. This problem also arises in the multi-disc camera. This makes it necessary for both the multi-tube and the multi-disc type cameras to register the images of the individual tubes or elements accurately.
In the case of the image pickup tube, the positioning of the photodetect areas can be corrected to some extent by adjusting the deflection signals of an electron beam. In the multi-tube camera of the prior art, characteristics of the image tube are utilized to register the photodetect areas of the three tubes by adjusting the current flow of a deflection signal generator 6 shown in FIG. 7.
Specifically, conditions such as the positions and aperture angles (which correspond to the zooming ratio, the F-number, and the distance to an object) are detected at first by a lens condition detector 7' which is composed of a potentiometer of a rotary encoder mounted in the lens. On the other hand, the aberration of the lens is changed with the position on a picture, the colors of the ray or the lens conditions such as the zooming ratio, the F-number, or the distance to an object. Therefore, this data is stored in advance in a memory/calculator of the registration discrepancy 7. On the basis of this stored data, the registration discrepancies at the individual picture positions are calculated from the lens conditions obtained from the lens condition detector 7'. On the basis of these registration discrepancies, the deflection signal generator 6 corrects the problem modifying the current of the deflection signal (as disclosed on pp. 40 to 47 of TV Association, Vol. 1.36, No. 10 (1982).
Thus, in a camera using the image pickup tube, the position of the photodetect area can be corrected to some extent by adjusting the deflection signal of the electron beam to allow for the fixed point of the image pickup tube. Moreover, the registration discrepancy of the chromatic aberration of the lens can also be adjusted to some extent.
In the solid state image pickup element, however, the image position is fixed on the photodetect plane so that the positional distortion cannot be freely corrected. As a result, the multi-disc camera is required to have a high degree of accuracy in the fixed pint registration of each image pickup element and in the fixing method or the characteristics of the lens used.
On the other hand, the present TB system is being examined to make the existing NTSC system finer. The picture element pitch of the solid state image pickup element used in this system is far smaller than that of the prior art and requires a high degree of accuracy in the fixed point of the element and in the lens. This high degree of accuracy makes adjustment difficult, raises the production cost, and requires an expensive lens.